When Ethernet® is used for communications, a MAC address (Media Access Control address) is employed as an address that is unique to each piece of hardware. In OSI (Open Systems Interconnection) reference models, the MAC address is an address in layer 2. The MAC address is also called the physical address, Ethernet® address, or Node ID.
A MAC address is 48-bit data. The IEEE manages the upper 24 bits of the MAC address, and these bits are called the OUI (Organizationally Unique Identifier). Manufacturers can assign their own values to the lower 24 bits. This system thus provides a unique MAC address on the network.
In the management of MAC addresses, a unique MAC address is embedded in a non-volatile memory such as an EEPROM (electrically erasable and programmable read-only memory) during manufacturing. To reduce the aforementioned burden of managing MAC addresses (management of uniqueness) during manufacturing, an IC containing unique information, such as a silicon serial number, may be used.
However, if the IC containing silicon serial number is used for managing MAC addresses, the same MAC address may be present in the network if the amount of information is reduced or processed. For example, this may happen when a 6-byte silicon serial number is processed to a 3-byte information to generate a MAC address.
If two or more devices in a network have the same MAC address, an Ethernet® frame sent by unicast transmission will not reach its intended destination, and communications, including TCP/IP, may not operate correctly.
On the other hand, the MAC address can be changed in some devices. This is disclosed in Patent Document 1. In this example, the MAC address to be set is searched for in the network before changing it.
If the MAC address does not exist in the network, a set request packet of SNMPv3 (Simple Network Management Protocol version 3) is generated and sent. The MAC address is then written to the non-volatile memory of the device receiving this packet. This device will then use this MAC address thereafter. SNMPv3 uses UDP (User Datagram Protocol) packets.
The method disclosed in Patent Document 1 is a system designed to change the MAC address of a specific device so as to rule out duplicate MAC addresses in a network where no duplicate MAC addresses exist. Since this system employs SNMPv3 as the communication means, communication itself cannot be correctly established in the first place if duplicate MAC addresses are present in the network. Therefore, duplication of MAC addresses cannot be resolved.    Patent Document 1: Japanese Patent Unexamined Publication No. 2006-197516.